The present invention relates to a tool management system and particularly to a system providing control of reticle stocking and sorting operations in a semiconductor fabrication system.
Depending on the type of IC device being manufactured, a wafer may be subjected to several photolithography processes as layers are formed successively to form the device. To perform the various photolithography processes, a semiconductor plant has a photolithography area comprising a number of steppers that utilize a cataloged library of reticles. The number of reticles that need to be readily available can easily exceed one thousand, due to the number of different products that can be manufactured in one facility, with each reticle having a replacement cost of about $1,500. The reticles are usually stored in a reticle storage system, centrally located within the photolithography area, and are cataloged by reticle identification number. The reticle(s) are transported via a conveyor system to the particular stepper awaiting a certain reticle. One problem with managing reticles is that they are very delicate structures and can be easily damaged in handling. They are also routinely inspected to ensure that they are still viable for use.
These reticles have not only high replacement cost, but also high maintenance cost. Reticles occupy storage and substantial floor space, creating considerable traffic congestion in the fabrication system.
The reticles are generally owned by customers rather than a fabrication plant. The fabrication plant bears the responsibility of maintaining the reticles, and lack authority to phase out or scrap reticles without customer permission.
FIG. 1 is a schematic view showing a conventional method of reticle management. Reticles are stored in online reticle storage 11, offline reticle storage 13, or reticle outlet 15. The reticles are then transported by transport devices 12, 14, and 16. The current position and other related information is stored in a reticle management center 17. When reticles are conventionally utilized in a fabrication process within a fabrication system 10, they are stored in online reticle storage 11 awaiting transport to a processing area. These reticles lie idle in the online reticle storage 11 not in use. When idle time of the reticles exceeds a preset time period, manual intervention is required to move these idle reticles from the online reticle storage 11 to the offline reticle storage 13. These reticles are moved back to the online reticle storage 11 when needed for fabrication processes. Generally, the activation of the idle reticles is initiated by a product order pertaining to these reticles. When the idle reticles stay in the offline reticle storage 13 longer than a preset time period, they should be moved from the offline reticle storage 13 to the reticle outlet 15. At the same time, a customer engineer 18 of the fabrication system 10 checks the reticle idle state from a reticle management center 17, informs the owner 19 (customer) of the reticles in this idle state and requests disposition of the reticles. If the customer wishes to take possession of the idle reticles, the reticles are returned. If the customer declines to take possession, the reticles are scraped shortly thereafter.
Such conventional reticle management system has several disadvantages.
First, the conventional system leads to redundant reticle transport among the online reticle storage 11, the offline reticle storage 13, and the reticle outlet 15. In the conventional system, idle reticles are moved from online to offline reticle storage when the idle time of the reticles exceeds a preset time period, and are returned to the online reticle storage 11 when required by any fabrication process. The transport of reticle from the online reticle storage 11 to the offline reticle storage 13 is executed manually, with idle time the sole factor impacting transport decisions. Thus, reticles can be characterized as idle and returned to the offline reticle storage, even though a pertinent process operation, requiring their use, may resume as soon as one day later. After the reticles reach the offline reticle storage, they are restored to the online reticle storage when the process operation resumes. This round trip in a short time consumes transport capacity of the fabrication system, and requires an excess of manual attention, lowering overall efficiency of the fabrication system.
Second, considerable communication is required when querying customers for disposition instructions for the reticles. Since reticles have high replacement cost and are of major importance in the fabrication process, disposition is deployed carefully, with erroneous disposition resulting in serious consequences. Generally, a decision regarding reticle disposition only follows repeated discussion and confirmation through complex paperwork and processes.
Third, there is no flexibility in setting the time limit for different customers and products. All reticles in the online reticle storage have the same idle time limits, as do the reticles in the offline storage, despite the fact that reticles may belong to different customers and pertain to different products, all with discrete needs and practices. Some customers may order frequently, some infrequently, and others sporadically. Similarly, different products are characterized by different order patterns. The conventional system assigns a single idle time limit to all reticles and passes over the above-mentioned differences without due attention.
Hence, there is a need for a reticle management system that addresses the inefficiency arising from the existing technology.